LIPOSOME COMPRISING A MEMBRANE WALL COMPOSED OF A TREHALOSE FATTY ACID ESTER

Abstract: A surfactant containing at least one trehalose-6-fatty acid ester represented by general formula (I) (wherein R represents C 8 -C 22 (un)saturated acyl which may be substituted by OH, etc.) and excellent in surface activity and safety; an emulsion cosmetic containing the surfactant and a water-soluble polymer, excellent in prolonged storage stability and organoleptic characteristics, and reduced in skin stimulation, and having a beautiful appearance with a fine texture; and a liposome having a membrane wall comprising the trehalose ester and being excellent in physical and chemical stabilities such as prolonged preservability.

Description: The present invention relates to a liposome which is characterized in that it has a wall membrane formed from a trehalose fatty acid ester wherein the fatty acid of said trehalose fatty acid ester is a saturated or unsaturated fatty acid having 10-18 carbon atoms, and which is useful in drugs, quasi-drugs, cosmetics and so forth. Liposome is a closed vesicle whose wall membrane is composed of a lipid bilayer. Natural biomembrane is said to have lipid dyad membrane structure. The present liposeome has biomembrane-like structure. Therefore, it is expected that the liposome has high affinity with biocell membrane and has high potential as a drug carrier. Recently, the development of liposome formulations aiming at a drug delivery system has been desired not only in the fields of pharmaceticals, but in cosmetics. Phospholipid (lecithin) has been used as a liposome forming agent. This is excellent in safety, but is hardly used in practical applications because of its poor chemical and physical stabilities. In other words, chemical changes such as changes of color and smell occur in long-term storage in the case where liposome is prepared with phospholipid. Also, physical changes such as aggregation and precipitation occur after long-term storage or by rehydration after freeze-drying. Because of these problems, liposomes from phospholipid have not been put to practical use. It was tried to find other substance which has liposome-forming activity to solve these problems. For example, there are publications on dialkyl-type cationic surfactants such as dialkyldimethylammonium chloride (kunitake et al. J. Am. Chem. Soc., vol 99, pp860, 1977), POE-type nonionic surfactants such as polyoxyethylene cured castor oil (Japanese Patent Application Laid Open No.52-6375/1977, and No.59-16534/1984). Also, there are reported sucrose fatty acid esters(Japanese Patent Application Laid Open No.61-207324/1986), glucose fatty acid esters(Japanese Patent Application Laid Open No.4-300820/1991), and glucose alkylether(Japanese Patent Application Laid Open No.59-106423/1984), in which sugars are used as a hydrophilic group. However, the stability of these liposomes is not satisfactory. Also, in order to improve the stability of liposome, sugars such as trehalose are added to liposome(Japanese Patent Application Laid Open No.62-500102/1987, and No.62-501631/1987). Meanwhile, there are some report on trehalose fatty acid ester, such as a report on its synthesis (Chem. Pharm. Bull, 30(4), pp1169-1174(1982), a report aiming to use trehalose difatty acid ester as a surfactant (Japanese Patent Application Laid Open No.60-258195/1985 and No.62-91236/1987), and a report aiming to use it as an antitumor agent(Japanese Patent Application Laid Open No.61-289038/1986, Chem. Pharm. Bull., vol 25(7), pp1717-1724). Furthermore, from Angewandte Chemie International Edition, vol. 23, no. 2, (1984), pages 100-113 liposomes comprising a membrane wall composed of trehalose C 32 -C 36 -fatty acid ester are known. A further object of the invention is to provide a liposome which has excellent chemical and physical stabilities such as storage stability. The prersent invention is a liposome, characterized in that it has membrane wall composed of a trehalose fatty acid ester, wherein the fatty acid of said trehalose fatty acid ester is a saturated or unsaturated fatty acid having 10-18 carbon atoms. The present invention is a liposome, characterized in that it has membrane wall composed of trehalose C 10 -C 18 - difatty acid ester. The present invention will be explained further in details below. The trehalose fatty acid ester used in the invention can be obtained from trehalose and a fatty acid or ester thereof in a known synthesis method, such as by ester exchange reaction between trehalose and a lower alkyl ester of a fatty acid. The trehalose fatty acid ester can be produced, for example, in a method for the preparation of sucrose fatty acid esters disclosed in US Patent No.2893990 and No.3963699, Japanese Patent Application Laid Open No36-21717/1961 and No.53-6130/1978, all of which are incorporated herein by reference. Trehalose may be any of α,α-trehalose, α,β-trehalose or β,β-trehalose or mixtures of two or more of them. In these methods, a mixture of mono-fatty acid ester, difatty acid ester and tri- or more fatty acid ester of trehalose are obtained as reaction products. These products can be isolated by any conventional purification methods. However, the mixture of trehalose fatty acid ester can be used without any purification. As the trehalose fatty acid ester, preferred are trehalose poly-fatty acid esters, particularly diesters. The fatty acid to compose the trehalose fatty acid ester is a saturated or unsaturated higher fatty acid having 10-18 carbon atoms. Examples of those include trehalose caprate, trehalose undecanate, trehalose laurate, trehalose myristate, trehalose palmitate, trehalose stearate, trehalose undecylenate, trehalose oleate, trehalose linolate, trehalose linolenate, trehalose isostearate, trehalose monohydroxystearate, and trehalose ricinoleate. These fatty acids may be used alone or as a mixture. The diesters are not required to be of high purity, and the content of the diesters is preferably 30 wt.% or more, based on the total weight of the trehalose fatty acid ester. The liposome of the invention may contain unreacted raw materials, i.e. trehalose and fatty acid esters in such an amount as not to adversely affect the liposome formation. The liposome of the invention may be composed of a single species of trehalose fatty acid ester or a mixture of two or more species. The liposome of the invention may contain sterols, such as cholesterol and cholestanol, as a membrane stabilizer; dicetylphosphate, phosphatidic acid, ganglioside, stearylamine and so forth, as a charged substance; and α-tocopherol as an antioxidant. These substances may be added preferably in amounts of about 0.01 to about 2.0 weight parts per weight part of the trehalose fatty acid ester, but not limited to such a range. Any conventional methods for preparing a liposome can be used in the invention. For example, a vortexing method, a sonication method, a pre-vesicle method, an ethanol injection method, a French press method, an ether injection method, an annealing method, a W/O/W emulsion method, a reverse phase evaporation method and so forth can be mentioned. Any of them or any combination of them can be used, but not limited to these. Preparation in a vortexing method or sonication method will be explained below. A trehalose fatty acid ester and a membrane stabilizer and any optional substances are dissolved in an organic solvent, preferably chloroform, and the organic solvent was evaporated out to form a thin membrane composed of the trehalose fatty acid ester. A buffer solution in which a water-soluble component, etc. were dissolved was added, and was vortexed at or above its phase transition temperature to strip off the membrane. At this point of time, a polylayer liposome (MLV) was formed. Then, a single layer liposome (SUV) was obtained by sonication, if desired. The liposome of the invention may contain ordinary pharmaceutical components such as water-soluble polymers, polyvalent alcohols, preservatives and chelating agents. Examples This invention will be explained further in details in the following Examples, but not limited to those. Example A One hundred mg of trehalose dilaurate was charged in a 50 ml volume eggplant type flask, and dissolved by adding 5 ml of chloroform. Then, this flask was set on a rotary evaporator, and the solvent was evaporated out slowly so that a thin membrane of trehalose dilaurate was formed on the inner wall of the flask. The inside of the flask was then evacuated by a vacuum pump to be dried for additional 3 hours. Four millilitres of distilled water were added and shaked at 60 °C to strip off the thin membrane. Thus, an aqueous cloudy liquid was obtained. In observation by a polarizing microscope (x 400), particles of 1-10 µm in diameter were seen with "closed lamella structure" which is characteristic of MLV. This aqueous liquid was stained with phosphotungstic acid. In observation by a transmission electron microscope (x 100,000), closed vesicles having about five- to nine-layer membrane structure, i.e., liposomes, were observed. Then, this aqueous liquid was sonicated by a probe-type sonicator for 10 min. at 60 °C. In observation by a transmission electron microscope as above, SUV's of 50 - 80 nm in particle diameter were observed. Example B Liposomes were prepared in accordance with the procedures of Example A except that a 100 mM aqueous carboxyfluorescein (CF) solution was substituted for distilled water. After MLV's were formed, a liposome solution was gel filtrated to remove CF present in the exterior phase (i.e., not contained in liposomes). Then, liposomes were destroyed by adding an aqueous Triton X-100 solution. By measuring the fluorescence intensities before and after the addition of the aqueous Triton X-100 solution, it was confirmed that CF was trapped in the interior phase (inside the liposomes). The retaining efficiency was 15.5%. Example C Liposomes were prepared in accordance with the procedures of Example A except that trehalose dipalmitate was substituted for trehalose dilaurate. In observation by an electron microscope, it was confirmed that MLV's and SUV's were formed. Example D A mixture of 20mg of trehalose monomyristate, 60mg of trehalose distearate and 20mg of trehalose tri- or more stearate was added to 8 ml of ethanol and dissolved by heating at 50 °C. The solution was pressure injected into distilled water heated at 60 °C by a syringe. As a result, an aquous translucent solution was obtained. In observation by an electron microscope as in Example A, it was confirmed that SUV's were formed. The results of Examples A-D showed that trehalose fatty acid esters could form liposomes. In the following, the liposome of the invention was compared with the liposome of prior art for stability. Example E One gram of Trehalose diundecylenate, 0.5g of cholesterol and 0.2g of dicetylphosphate were charged in a 200 ml volume eggplant type flask and dissolved by adding 10 ml of chloroform. Then, this flask was set on a rotary evaporator, and the solvent was evaporated out slowly so that a thin membrane was formed on the inner wall of the flask. The inside of the flask was then evacuated by a vacuum pump to be dried for additional 3 hours. One hundred millilitres of distilled water were added and shaked at 60 °C to strip off the thin membrane. Then, this solution was sonicated by a probe-type sonicator for 10 min. at 60 °C to prepare SUV's. In observation by a dynamic light scattering method, the particle diameter was 62 nm. Example F A mixture of 0.2g of trehalose monomyristate, 0.6g of trehalose distearate and 0.2g of trehalose tri- or more stearate was added to 10 ml of ethanol and dissolved by heating at 50 °C . The solution was pressure injected into distilled water heated at 60 °C by a syringe to prepare SUV's. In observation by a dynamic light scattering method, the particle diameter was 73 nm. Comparative Example A SUV's were prepared in accordance with the procedures of Example E except that hydrogenated soybean lecithin was substituted for trehalose diundecylenate. In observation by a dynamic light scattering method, the particle diameter was 59 nm. Comparative Example B SUV's were prepared in accordance with the procedures of Example E except that sucrose diundecylenate was substituted for trehalose diundecylenate. In observation by a dynamic light scattering method, the particle diameter was 70 nm. After storing the liposomes which were prepared in Examples E and F and Comparative Examples A and B for 3 months at 40 °C, the changes of color, smell and particle diameter were examined. The results are as shown in Table A. Further, the liposomes were each freeze-dried and rehydrated, and then their particle diameters were measured. The results are as shown in Table B. Conditions after 3 Month-Storage at 40°C color change foul smell particle diameter,nm Example E no no 75 Example F no no 80 Comp.Ex.A yellowish egg smell 159 Comp.Ex.B no no 142 Particle Diameter After Freeze-Drying and Re-Hydration particle diameter,nm Example E 72 Example F 77 Comp.Ex. A 189 Comp.Ex. B 112 Tables A and B show that the liposomes of the invention showed superior stability compared with the liposomes of the prior art prepared from hydrogenated soybean lechitin or sucrose fatty acid ester. The results of Examples E and F were better than those of Comparative Example B. The reason of these results is considerably that the molecular structure of trehalose diundecylenate is more symmetrical than that of sucrose diundecylenate, which contributes to the stability of the liposomes. The liposome of the invention has excellent stability. Also, the liposome of the invention can properly envelop water-soluble or oil-soluble drugs and does not suffer from chemical and physical changes. Therefore, the liposome of the invention is useful in the fields of drugs, quasi-drugs, cosmetics and so forth, and can provide liposome formulations suitable for injection drugs, oral medicines, external medicines, lotions, emulsions, creams, essences, and hair tonics.

Claims: A liposome comprising a membrane wall composed of a trehalose fatty acid ester, wherein the fatty acid of said trehalose fatty acid ester is a saturated or unsaturated fatty acid having 10-18 carbon atoms. The liposome as claimed in claim 1, wherein said trehalose fatty acid ester is a trehalose difatty acid ester. The liposome according to claim 1, wherein the fatty acid of which said trehalose fatty acid ester is constituted comprises a hydroxyl group. The liposome according to claim 1 comprising a membrane wall mainly composed of at least one trehalose fatty acid ester selected from the group consisting of trehalose dilaurate, trehalose dipalmitate, trehalose diundecylenate, trehalose dimyristate and trehalose distearate.

Inventors: IKEMOTO TAKESHI, INOUE YOH-ICHI, MINAMINO HIROMI, SUMIDA YASUSHI, IKEMOTO, TAKESHI, INOUE, YOH-ICHI, MINAMINO, HIROMI, SUMIDA, YASUSHI
Applicants: KANEBO LTD, KANEBO LTD.
Application year: 1994
Main classification: A61K9
IPC codes: B01F17, A61K9, A61K8, A61Q19, A61K47, C11D1, B01J13, A61Q5